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This is why geckos can climb walls and you can't

A new study by the University of Cambridge's Department of Zoology has compared 225 different climbing creatures to reveal that the ability to scale vertical surfaces using adhesive pads is one that's strictly limited to smaller animals.

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Dr. David Labonte and his team estimated that for a human to crawl up a wall, Spider-Man style, 40 percent of their body's surface -- or 80 percent of their front -- would have to be covered by adhesive pads. As the scientists point out, that would be "unmanageably large", but they believe that their findings "have implications for the feasibility of large-scale, gecko-like adhesives" as a man-made technology.

The study, which included insects, frogs, spiders, lizards and even a mammal -- the Madagascar sucker-footed bat (Myzopoda aurita) -- shows that geckos have 200 times more of their body's surface area covered in adhesive pads than tiny mites.

"As animals increase in size, the amount of body surface area per volume decreases -- an ant has a lot of surface area and very little volume, and an elephant is mostly volume with not much surface area," Labonte explained. "This poses a problem for larger climbing animals because, when they are bigger and heavier, they need more sticking power, but they have comparatively less body surface available for sticky footpads. This implies that there is a maximum size for animals climbing with sticky footpads – and that turns out to be about the size of a gecko."

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Although, according to the study "larger organisms can develop strongly folded internal surfaces for enhanced diffusion [...] in many cases areas cannot be folded so that their enlargement is constrained by anatomy".

And for humans, that creates difficulties. "If a human, for example, wanted to climb up a wall the way a gecko does, we’d need impractically large sticky feet – and shoes in European size 145," wrote senior author Walter Federle.